1. Field of the Invention
The present invention relates to a keying pulse processing circuit and, more particularly to, a keying pulse processing circuit for use in a noise canceler for a CATV converter.
2. Description of the Prior Art
The keying signal transmitted into the keying, pulse processing circuit is a group of pulse signals having information necessary to descramble a scrambled image signal.
A conventional keying pulse processing circuit will be described with reference to the block diagram shown in FIG. 3. A keying pulse signal S1 applied from an input terminal 1 is shaped into a rectangular waveform signal S2 by a wave shaping circuit 2, and further processed into various necessary pulse signals by a pulse processing circuit 3 for use in a video system 4 and CPU 5.
However, in the above conventional set-up of the keying pulse processing circuit, when a keying signal having a noise signal is input, there has been such a problem that the keying signal is processed without removing the noise signal from the keying signal, and the processed signal is input into the next stage as a normal keying signal.